Thermal cracking of hydrocarbons in the presence of added sulfur compounds and nitric oxide

ABSTRACT

1. A METHOD FOR THE THERMAL CRACKING OF MIXTURES OF NORMALLY LIQUID HYDROCARBONS HAVING AT LEAST 5 CARBON ATOMS IN THE MOLECULE CHARACTERIZED BY INCREASED CONVERSION TO LOWER MOLECULAR WEIGHT PRODUCTS AND DECREASED PRODUCTION OF PRODUCTS BOILING IN THE SAME RANGE AS SAID NORMALLY LIQUID HYDROCARBON CHARGE MIXTURE WHICH COMPRISES ADDING SULFUR, A SULFUR COMPOUND SELECTED FROM THE GROUP CONSISTING OF CARBON DISULFIDE, CARBONYL SULFIDE, AMMONIUM SULFIDE, MERCAPTANS, ALKYL SULFIDES, ALKYL DISULFIDES OR MIXTURES THEREOF TOGETHER WITH NITRIC OXIDES TO A VAPORIZED STREAM OF SAID NORMALLY LIQUID HYDROCARBON CHARGE MIXTURE, THEREAFTER SUBJECTING THE RESULTING SULFUR AND NITRIC OXIDE-CONTAINING HYDROCARBON STREAM TO THERMAL CRACKING CONDITIONS AND RECOVERING THE THERMALLY CRACKED PRODUCTS.

United States Patent 3,848,017 THERMAL CRACKING OF HYDROCARBONS IN THEPRESENCE OF ADDED SULFUR COM- POUNDS AND NITRIC OXIDE Harold Shalit,Drexel Hill, Pa., assignor to Atlantic Richfield Company, Los Angeles,Calif. No Drawing. Filed Sept. 24, 1973, Ser. No. 400,482 Int. Cl. C07c3/30 U.S. Cl. 260-683 R 11 Claims ABSTRACT OF THE DISCLOSURE Theaddition of a combination of sulfur, a sulfur compound or mixture-sthereof and nitric oxide to a vaporized hydrocarbon charge stream giveshigh conversions of the hydrocarbon stream to lower molecular weighthydrocarbons in the subsequent thermal cracking of such stream ascompared with the conversions obtained in the absence of thesecompounds.

BACKGROUND OF THE INVENTION The pyrolysis or thermal cracking ofhydrocarbons as well as other organic compounds has, of course, beenknown and practiced for a great many years. As originally conceived thepurpose of thermal cracking was to convert norm-aly liquid heavyhydrocarbon stocks into those boiling in the gasoline range, but withthe advent of catalytic cracking which was far superior for thispurpose, thermal cracking was directed toward the production of C andlighter hydrocarbons for use as petrochemicals from normally liquidhydrocarbon mixtures such as naphthas and gas oils. The term normallyliquid is conventionally used to describe hydrocarbons liquid at ambient(room) temperature and atmospheric pressure. Thus C to C s are notincluded and often isopentane is excluded since it 'boils at about 85 F.and therefore is frequently removed from normally liquid charge stocks.The concurrent production of pyrolysis gas oils and naphthas representeda penalty to the process since these were in the same boiling range asthe charge hydrocarbons and therefore did not constitute an improvement.

Many early proposals were made to improve the conversion in thermaldecomposition reactions, for example, W. L. Roth and G. K. Rollefson ina paper in Journal American Chem. Soc., Vol. 64, p. 1707 et seq. (July,1942) showed an improvement in the thermal decomposition of acetaldehydeby the use of hydrogen sulfide and nitric oxide to produce methane andcarbon monoxide.

Two recent patents, United States Nos. 3,751,514 and 3,751,516 show,respectively, the conversion of isobutane into isobutylene and propyleneand the conversion of n-butane into propylene using as a homogeneouscatalyst in each process asulfur compound such as hydrogen sulfide,ammonium sulfide, a mercaptan or the like or a bromine compound. Thesecharge hydrocarbons, i.e. isobutane and n-butane are, however, valuableas chemicals and so such processes are not particularly desirable. Theydo not show combinations of these catalysts with nitric oxide nor dothey show thermal cracking of heavy hydrocarbon charge stocks.

Since most normally liquid hydrocarbon charge stocks contain sulfurcompounds and many contain nitrogen compounds as well, it was surprisingto find that if a combination of sulfur or a sulfur compound and nitricoxide was added to the vaporized normally liquid hydrocarbon chargeprior to thermal cracking, thereafter in the thermal cracking processmarkedly higher conversions to lighter hydrocarbons are obtained ascompared with the thermal cracking in the absence of these compounds.

The results obtained with the combination of sulfur, the sulfur compoundor mixture-s thereof and nitric oxide "ice in relatively small amounts,i.e. up to a total of 9 mole percent for the combination are equivalentto the results obtained with from 10 to 50 mole percent of the sulfur orsulfur compound alone. The combination of the sulfur or sulfur compoundwith the nitric oxide has been found to give results superior to thoseobtained by the use of either of these alone.

SUMMARY OF THE INVENTION In accordance with this invention a combinationof sulfur, carbon disulfide, carbonyl sulfide, ammonium sulfide,hydrogen sulfide, mercaptans, alkyl sulfides, alkyl disulfides ormixtures thereof with nitric oxide is added to a vaporized normallyliquid hydrocarbon charge before the charge is heated to crackingtemperature. The amount of the sulfur or sulfur compound which is addedcan range from about 2 mole percent to 5 mole percent based on the totalcharge and the amount of nitric oxide can range from about 1 molepercent to 4 mole percent based on the hydrocarbon charge. The resultsobtained in utilizing this combination of compounds are higherconversion to the lower boiling hydrocarbons particularly in the C to Crange with the corresponding reduction in the amount of material boilingin the same range as the feed stock.

It is an object of this invention therefore to provide an improvedmethod for the thermal cracking of normally liquid hydrocarbons.

It is another object of this invention to provide a method for thethermal cracking of normally liquid hydrocarbons wherein higherconversions to lower molecular weight products are obtained with acorresponding reduction in the amount of products boiling in the samerange as the feed stock.

It is another object of this invention to provide an improvedhydrocarbon thermal cracking process utilizing a combination of sulfur,a sulfur compound, mixtures of sulfur with a sulfur compound or mixturesof sulfur compounds with nitric oxide added to the hydrocarbon charge.

Other objects of this invention will be apparent from the description ofthe invention and from the claims.

DESCRIPTION OF THE INVENTION The charge stocks which can be used in themethod of this invention include those ranging from stabilized, i.e. thenormally gaseous hydrocarbons have been removed (C to C and in someinstances isopentane) crude oils to light naphthas, with preferredcharge stocks being the normally liquid gas oils and naphthas withhighly paraffinic light naphtha stocks being particularly amenable totreatment by the method of this invention. Naphthas or light naphthas asthe terms are used herein refer to fractions containing hydrocarbonsranging from those having 5 carbon atoms in the molecule, i.e.de-butanized and some de-isopentanized naphthas, to hydrocarbons boilingup to 400 F. to 420 The gas oils are higher boiling than naphthas andcan range from an initial boiling point of about 350 F., but generallyabove this tem perature, to an end point of about 650 F. or above. Theseranges are, of course, subject to variations in accordance with theparticular crudes being processed by the refiner.

The hydrocarbon charge can range from about 10 mole ercent to 50 molepercent based on the total charge with from 20 mole percent to 40 molepercent based on the total charge being preferred.

The sulfur or sulfur compounds which can be utilized in the method ofthis invention include sulfur, hydrogen sulfide, ammonium sulfide,carbon disulfide, carbonyl sulfide, the mercaptans, alkyl sulfides,alkyl disulfides and mixtures of these. The sulfur can be convenientlyadded by solution, for example, in carbon disulfide. The mercaptans arecharacterized by having the formula RSH wherein R is an unsubstitutedalkyl radical having from 1 to 8 carbon atoms. The alkyl sulfides arecharacterized by the formula RSR wherein R and R may be the same of from2 to 8 carbon atoms. The alkyl disulfides are characterized by theformula RSSR', wherein R and R may be the same or differentunsubstituted alkyl radicals having a total of from 2 to 8 carbon atoms.Although higher molecular weight mercaptans, sulfides and disulfides areoperable, they are not preferred, and the most preferred mercaptans,sulfides and disulfides are those having from 1 to 4 carbon atoms. Thesulfur or sulfur compound or mixture together with the nitric oxide isadded to the charge stock which is in vaporized form before such stockis heated to cracking temperatures. The sulfur or sulfur compounds addedcan range in amounts from about 2 mole percent to 5 mole percent basedon the total charge and the nitric oxide is added in amounts rangingfrom 1 mole percent to 4 mole percent based on the total charge.Preferably the amount of sulfur or sulfur compound ranges from 3 to 5mole percent and the amount of nitric oxide ranges from 1 to 3 molepercent. The cracking temperatures employed can range from about 675 C.to 800 C. with a more preferred range being from 700 C. to 775 C.Pressures ranging from 0.5 to 5 atmospheres, preferably from 1 to 2atmospheres, and contact times of from 0.1 to 2.0 seconds, preferablyfrom 0.5 to 1.2 seconds, are employed. Diluents such as steam ornitrogen can be used to reduce the partial pressure of the mixed chargein amounts ranging from about 5 to 80 mole percent of the total charge.

In the Examples which follow all of the runs were carried out in atubular quartz reactor packed with tabular alumina granules for improvedheat transfer. The tube was heated externally by an electric furnace,and temperatures were measured axially at various points down the bed.The products (except the non-condensibles) were collected in Dry-Icetraps and were analyzed by gas chromatography.

The Examples which follow are provided for illustrating the invention inadditional detail but are not to be construed as limiting.

EXAMPLE I Comparative cracking runs were carried out on a West Texasnaphtha having the composition and properties shown in Table I.

TABLE I Composition, weight percent:

Alkanes:

C i-C 3.3 11-0 29.3 (3 29.3 C7 8-8 0,, 5.4 (3 0.2 C10 0 Cycloalkanes12.7 Aromatics:

C 1.5 O; 0.8 C 2.5 C 0.1 Total 100.0

Properties:

Density at 20 C 0.6742 API gravity at 60 F 77.1 Average molecular weight83.13

The conditions used and results obtained are shown in Table II.

It can be seen from these results that the nitric oxide serves as anactivator for the sulfur compound. In the absence of either the sulfurcompound or nitric oxide the conversion shown in Run N0. 1 is obtained.The addition of a relatively small amount of sulfur compound gives amarked increase in conversion, Run No. 2 compared with Run No. 1. In theabsence of nitric oxide the increase in conversion between 3.66 percentH S (Run No. 2) and 14.06 percent (Run No. 4) is almost 20 percent,i.e., the H 8 is more than 4 times as great in Run No. 4 as in Run No. 2but when only 1.42 percent nitric oxide i added to 3.39 percent H 8 theconversion is increased 10 percent comparing Run No. 2 with Run No. 3.

EXAMPLE II TABLE III Run number -5 6 Reaction conditions:

Tcmperature, C 754 755 Contact time (seconds) 1. 0 1.0 Feed gascomposition:

Naph the, volume percent 29. 49 29. 74 Nitrogen volume percent 68. 2365. 14 Has volume percent 0 3. N0 volume percent 2. 28 1. 32 Conversion,wt. percent 76. 5 90. 6 Production distribution, pounds per pounds ofnaphtha fed:

Hydrogen 0. 84 0. 71 11. 5 13. 3 26. 6 17. 4 6. 7 19. 8 16. 9 22. 7 0 04. 2 6. 2 7. 6 8. 5 1. 7 1. 6 20. 7 3. 7 1. 7 3. 2 0. 3 0. 7 0. 7 1. 80. 5 0. 4 0. 46 0. 41

The conversion obtained with nitric oxide only, Run No. 5, issubstantially the same as that obtained by thermal cracking alone atthis temperature which gives a conversion of almost 79 weight percentwhich is not a significant difference. The results obtained in Run No. 6are substantially the same as obtained when 20 mole percent hydrogensulfide only is used for increasing the conversion.

The results obtained as shown in the foregoing examples show that theaddition of small amounts of nitric oxide greatly reduces the amount ofsulfur compound needed to give an increased conversion.

EXAMPLE III A series of runs were made on the same West Texas naphthaused in Examples I and II comparing the conversions obtained by (1)straight thermal cracking, (2) cracking in the presence of 20 molepercent hydrogen sulfide (based on total feed) and (3) cracking in thepresence of approximately 2 mole percent nitric oxide and 5 mole percenthydrogen sulfide based on total feed. In each run the naphtha amountedto about 29.5 mole percent and the remainder of the feed was nitrogen asthe diluent gas.

It was found that at about 700 C. the increase in conversion using 20mole percent hydrogen sulfide over straight thermal cracking amounted toabout 30 weight percent while the 2 mole percent nitric oxide plus molepercent hydrogen sulfide combination exceeded straight thermal crackingconversion by about 23 weight percent. At about 725 C. the 20 molepercent hydrogen sulfide conversion and the 2 mole percent nitric oxide5mole percent hydrogen sulfide gave about the same con version which wasabout 21 to 22 weight percent higher than the straight thermal cracking.At 775 C. the increase still remains important being about 8 weightpercent.

Accordingly, the utility of this invention is clearly demonstrated,namely that the use of small quantities of nitric oxide in combinationwith a sulfur compound or sulfur greatly reduces the quantity of sulfurcompound required to give the desired increase in conversion in thermalcracking processes.

I claim:

1. A method for the thermal cracking of mixtures of normally liquidhydrocarbons having at least 5 carbon atoms in the moleculecharacterized by increased conversion to lower molecular Weight productsand decreased production of products boiling in the same range as saidnormally liquid hydrocarbon charge mixture which comprises addingsulfur, a sulfur compound selected from the group consisting of carbondisulfide, carbonyl sulfide, ammonium sulfide, mercaptans, alkylsulfides, alkyl disulfides or mixtures thereof together with nitricoxides to a vaporized stream of said normally liquid hydrocarbon chargemixture, thereafter subjecting the resulting sulfur and nitricoxide-containing hydrocarbon stream to thermal cracking conditions andrecovering the thermally cracked pro ducts.

2. The method according to claim 1 wherein said sulfur, sulfur compoundsor mixtures thereof range from about 2 mole percent to 5 mole percentbased on the total charge, the nitric oxide ranges from about 1 molepercent to 4 mole percent based on the total charge and a gaseousdiluent ranges from about 5 to 80 mole percent based on the totalcharge.

3. The method according to claim 2 wherein said sulfur, sulfur compoundsor mixtures thereof range from about 3 to 5 mole percent based on thetotal charge and the nitric oxide ranges from about 1 to 3 mole percentbased on the total charge.

4. The method according to claim 1 wherein said thermal cracking iscarried out at temperatures in the range of from 675 C. to 800 C.

5. The method according to claim 4 wherein said normally liquidhydrocarbon charge mixture is a naphtha having hydrocarbons of 5 carbonatoms and ranging up to 6 hydrocarbons boiling up to 400 F. to 420 F.and said sulfur compound is hydrogen sulfide.

6. The method according to claim 4 wherein said normally liquidhydrocarbon charge mixture is a gas oil fraction having an initialboiling point of at least 350 F. and said sulfur compound is hydrogensulfide.

7. The method according to claim 5 wherein said naphtha ranges fromabout 10 mole percent to 50 mole percent based on the total charge.

8. The method according to claim 6 wherein said gas oil ranges fromabout 10 mole percent to 50 mole percent based on the total charge.

9. A method for the thermal cracking of normally liquid hydrocarbonmixtures selected from the group consisting of naphthas havinghydrocarbons ranging from at least 5 carbon atoms and ranging up tohydrocarbons boiling up 400 F. to 420 F. and .gas oils having an initialboiling point of at least 350 F. characterized by increased conversionto lower molecular weight products and decreased production of productsboiling in the same range as said normally liquid hydrocarbon chargemixture, said charge mixture ranging from 10 mole percent to 50 molepercent based on the total charge, which comprises adding from 1 molepercent to 5 mole percent based on the total charge of hydrogen sulfideand from 1 mole percent to 4 mole percent based on the total charge ofnitric oxide to a vaporized stream of said hydrocarbon charge mixture,thereafter subjecting the resulting hydrogen sulfide and nitricoxide-containing hydrocarbon stream to thermal cracking at temperaturesin the range of from about 675 C. to 800 C. and recovering the thermallycracked products.

10. The method according to claim 9 wherein said total charge containsfrom about 5 to 30 mole percent of nitrogen or steam as a diluent.

11. The method according to claim 10 wherein said thermal cracking is attemperatures in the range of from 700 C. to 775 C.

References Cited UNITED STATES PATENTS 3,803,259 4/1974 Porchey et a1.260--683 2,188,638 1/1940 Atwell 260683.3 3,403,192 9/1968 Vadekar etal. 260683.3 2,143,014 1/1939 Klein 260683.3 2,714,085 7/ 1955 Thackeret a1. 208113 3,308,056 3/ 1967 Schultz 208128 2,435,760 2/ 1948 Thackeret a1. 208113 2,321,604 6/1943 Kalichevsky et a1. 2081 14 2,343,9273/1944 Roberts 208113 DELBERT E. GANTZ, Primary Examiner C. E. SPRESSER,J 11., Assistant Examiner US. Cl. X.R.

1. A METHOD FOR THE THERMAL CRACKING OF MIXTURES OF NORMALLY LIQUIDHYDROCARBONS HAVING AT LEAST 5 CARBON ATOMS IN THE MOLECULECHARACTERIZED BY INCREASED CONVERSION TO LOWER MOLECULAR WEIGHT PRODUCTSAND DECREASED PRODUCTION OF PRODUCTS BOILING IN THE SAME RANGE AS SAIDNORMALLY LIQUID HYDROCARBON CHARGE MIXTURE WHICH COMPRISES ADDINGSULFUR, A SULFUR COMPOUND SELECTED FROM THE GROUP CONSISTING OF CARBONDISULFIDE, CARBONYL SULFIDE, AMMONIUM SULFIDE, MERCAPTANS, ALKYLSULFIDES, ALKYL DISULFIDES OR MIXTURES THEREOF TOGETHER WITH NITRICOXIDES TO A VAPORIZED STREAM OF SAID NORMALLY LIQUID HYDROCARBON CHARGEMIXTURE, THEREAFTER SUBJECTING THE RESULTING SULFUR AND NITRICOXIDE-CONTAINING HYDROCARBON STREAM TO THERMAL CRACKING CONDITIONS ANDRECOVERING THE THERMALLY CRACKED PRODUCTS.